A database organized in terms of a relational model is a relational database. The relational model provides a declarative method for specifying data and queries. Users may directly state what information the database contains and what information they want from the database, wherein a database management system describes data structures for storing the data and retrieval procedures for answering queries.
A relational database is generally a database that is treated as a set of tables and manipulated in accordance with the relational model of data. It contains a set of objects used to store, manage, and access data. Examples of such objects are tables, views, indexes, functions, triggers, and packages.
A partitioned relational database is a relational database whose data is managed across multiple partitions (also called nodes). This separation of data across partitions is transparent to users of most Structured Query Language (SQL) statements. Some data definition language (DDL) statements take partition information into consideration. DDL may be referred to as a subset of SQL statements that are used to describe data relationships in a database.
IBM® DB2® is a relational model database server developed by International Business Machines Corporation. (IBM and DB2 are trademarks of International Business Machines Corporation in the United States or other countries.) DB2 is organized around a hierarchy of database objects. The highest-level object in the hierarchy is a system, which represents an installation of DB2. A control center maintains a list of known systems and records information needed to communicate with each system (for example, network address, operating system, communication protocol, etc.). A system can have one or more DB2 instances, each of which can manage one or more databases.
An “instance” or “database manager” is a DB2 structure that manages data, controlling what can be done to the data and managing assigned system resources. Each instance is a complete environment, containing all the database partitions defined for a given parallel database system. An instance has its own databases (which other instances generally cannot access), and all its database partitions share the same system directories. An instance also has separate security from other instances on the same computing device, machine or system.
A relational database is organized into parts called table spaces and presents data as a collection of tables. A table consists of a defined number of columns and any number of rows. Each database includes a set of system catalog tables that describe the logical and physical structure of the data, a configuration file containing the parameter values allocated for the database, and a recovery log with ongoing transactions and transactions to be archived.
A table space is a storage structure containing tables, indexes and data. In creating a table, certain objects such as indexes and large object data may be kept separately from the rest of the table data. A table space can also be spread over one or more physical storage devices. A database partition group is a set of one or more database partitions. Creating tables for a database generally necessitates first creating a database partition group where the table spaces will be stored, and then table space for storage of the tables.
Table spaces generally consist of containers that describe where objects are stored. Examples of containers include a directory name, a device name, a file name and a subdirectory in a file system. When data is read from table space containers, modified, or held during processing, it is placed in an area of memory called a buffer pool. A buffer pool is associated with a specific table space, thereby allowing control over which data will share the same memory areas for data buffering.